Two storms of significance will be affecting New Zealand’s weather in the days ahead, starting today.

Both bring a risk of severe weather, with the first storm almost becoming a “weather bomb” – that’s when the air pressure at the centre of the storm drops 24 hectopascals (hPa) in 24 hours – basically dropping one per hour.

STORM 1 – Sunday PM to Tuesday AM.
WeatherWatch.co.nz says Storm 1 is currently rapidly deepening in the north Tasman Sea and will be very close to reaching weather bomb criteria, with the central air pressure dropping over 20 hPa in the 24 hours from noon Sunday to noon Monday. Weather bomb (a term used so incorrectly by NZ’s news media it’s been noted in Wikipedia for years now) is the short way of saying the technical term: bombogenesis. It only relates to a low pressure system that technically loses 24hPa of air pressure within 24 hours. So this rapidly developing Tasman Sea storm is close – but not quite there. It shows, however, just how explosive this Tasman Sea system is.

Storm 1 today is tracking from north to south down the Tasman Sea and isn’t expected to make ‘landfall’ in NZ, but will be very close to Fiordland by Monday night. The worst of this storm looks set to remain mostly at sea – but strong winds gusting to gale with heavy rain in the north and west are the main features and will brush both main islands of NZ – MetService already has severe weather watches in force. This offshore storm will also help generate dangerous beach conditions on the western side of the nation.

STORM 2 – Tuesday PM to Friday
This is another low pressure zone but this time tracking from west to east – or put another way, it’s coming from Australia to NZ and follows so closely behind Storm 1 it gets caught up in the same orbit. This will see Storm 2 ‘stealing’ some of the energy from Storm 1, to create a new really big and very deep low pressure zone in the south Tasman Sea by mid this week.

Storm 2, on Wednesday morning, is currently forecast to have air pressure near Fiordland of just 959hPa – incredibly rare to see low pressure that deep near NZ and is more akin to a major Southern Ocean storm down near Antarctica – or that of a tropical cyclone to our north.

Also, with Storm 2 tracking sideways across the map towards NZ, it means Storm 2 will likely have a more significant impact on the NZ area as it more directly moves in.

At RuralWeather.co.nz you can see hourly Barometric pressure for the next 10 days ahead (under Detailed Data). This shows locations in Southland dropping into the 970hPa range on Wednesday as Storm 2 moves in.

Storm 2 will peak early on Wednesday morning – then as it moves into NZ it will weaken slowly, but will take until the weekend to clear off NZ to the east.

WeatherWatch.co.nz expects MetService to issue a number of warnings and watches in the days ahead covering severe gales, heavy rain, thunderstorms and dangerous waves. It’s going to be a busy week ahead weather-wise.